Two subcellular fractions involved in the development of the ovum in aves and mammals are under investigation. One fraction is the lining body that participates in synthesis and initial storage of protein during early oogenesis and intimate oocyte - follicle cell contact. We are studying its capacity to synthesize protein. Other fractions are the inner vitelline secreted by follicle cells and the outer vitelline secreted by oviductal cells. Following ovulation these secretions interdiffuse and form the surface envelope of the oocyte. We are studying the interactions of these secretions. The high nucleotide phosphohydrolase activities in the oviductal secretions and the roles of these exzymes in final oval maturation.